Hi,
I am a Master's student at Colorado State University, and I am getting 
ready to do some sulfur isotope work in a subalpine wetland complex.  We 
also have some nitrogen isotope work in forest soil-water starting up.  
We are interested in the isotopes of sulfur on sulfate and nitrogen on 
nitrate, and are currently running our water samples through anion 
exchange resin to adsorb the sulfate or nitrate.  The waters we are about 
to begin sampling have high DOC (about 10mg/L) and this will interfer 
with the anion adsorption.  A cation column preceeding the anion column 
cannot remove enough DOC, and we have thought about using organic 
specific resin (XAD8) or activated carbon.  But, we have also thought 
about some sort of membrane which would selectively remove the DOC and 
allow the water and our anions to move through and adsorb onto the anion 
exchange resin.  I am interested if anyone might know of something like 
this that work.  It seems as if most reverse osmosis-type membranes 
remove everything, and that would not be good...

any suggestions?
Cyndi Brock